Structural Chemistry

, Volume 15, Issue 3, pp 237–245

Conformational Analysis of Guaianolide-Type Sesquiterpene Lactones by Low-Temperature NMR Spectroscopy and Semiempirical Calculations

  • Slobodan Milosavljević
  • Ivan Juranić
  • Vanja Bulatović
  • Slobodan Macura
  • Nenad Juranić
  • Hans-Heinrich Limbach
  • Klaus Weisz
  • Vlatka Vajs
  • Nina Todorović
Article

Abstract

Conformational analysis of 9α-acetoxycumambrine A 1 and 8-O-isobutiryl-9α-acetoxycumambrine B 2 was carried out by low-temperature NMR studies. Results suggested that lactones 1 and 2 are mixtures of two distinctive conformers, I and II. Based on low-temperature 1H NMR spectra, in four solvents, the thermodynamic parameters of I ⇌ II exchange process were assessed. Energy of activation of I → II reaction was obtained by dynamic NMR simulations for both compounds. Results revealed that conformational exchange of lactones 1 and 2 occurs due to “chair ⇌ twisted chair” interconversion of a heptane ring. The same PM3 semiempirical method was applied for geometry optimization of lactones 1 and 2, as well as of 9α-hydroxycumambrine A 3, 9α-acetoxycumambrine B 4, and cumambrine B 5.

Guaianolides cumambrine conformations low-temperature NMR dynamic NMR PM3 semiempirical calculations 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

Copyright information

© Plenum Publishing Corporation 2004

Authors and Affiliations

  • Slobodan Milosavljević
    • 1
  • Ivan Juranić
    • 1
  • Vanja Bulatović
    • 2
  • Slobodan Macura
    • 3
  • Nenad Juranić
    • 3
  • Hans-Heinrich Limbach
    • 4
  • Klaus Weisz
    • 4
  • Vlatka Vajs
    • 5
  • Nina Todorović
    • 5
  1. 1.Faculty of ChemistryUniversity of BelgradeBelgradeSerbia and Montenegro
  2. 2.Institute for Medicinal Plant Research “Dr. Josif PančićBelgradeSerbia and Montenegro
  3. 3.Department of Biochemistry and Molecular BiologyMayo FoundationRochester
  4. 4.Institut für ChemieFreie Universität BerlinBerlinGermany
  5. 5.Institute for Chemistry, Technology and MetallurgyBelgradeSerbia and Montenegro

Personalised recommendations